The present invention relates to copiers and in particular to test equipment for determining the amount of developer in a copier.
It is known (for example, the RL-612 copier by Monroe) to employ a photosensitive drum onto which toner is deposited by a developing roller. Magnetically held on this developing roller are metallic carriers impregnated with toner. The toner is electrostatically transferred from the roller to the drum in accordance with the pattern of electrostatic charges on the drum, to produce a preliminary image. In this known copier the density of the toner is measured by a swinging lever attached in the toner bin but spaced from the drum. As the developer travels it urges the lever into electrically conductive brushes. Should the developer have insufficient toner, its weight will decrease and the lever will move accordingly. In this manner, the lever can sense whether it is necessary to add toner to the developer as copies are being produced.
An important consideration is accurately adding sufficient developer to the copier initially. A known technique for adding developer requires estimating the duty cycle of contact by the lever and brushes. A serviceman is required to judge when the duty cycle is about 90%, a 90% duty cycle being deemed to represent the correct volume of developer. While an indicator light can display the state of the lever relative to the brushes, it is often difficult for the serviceman to determine whether the duty cycle is actually 90% and his judgment becomes a matter of opinion which may vary from serviceman to serviceman.
Accordingly, there is a need for a simple, effective and accurate apparatus and method for determining whether a copier has the required amount of developer.